1. Field of the Invention
The present invention relates to a non-contacting position detecting apparatus, and particularly to a non-contacting position detecting apparatus suitable for use with a non-contacting three-dimensional measuring instrument which can perform a reliable and accurate measurement of coordinates of various portions of an outer profile of a subject to be measured.
2. Description of Background Art
Three-dimensional measuring instruments which detect a three-dimensional shape as three-dimensional coordinate data are disclosed, for example, in U.S. Pat. Nos. 3,722,842, No. 4,102,051, No. 4,149,317 and No. 4,282,654.
The three-dimensional measuring instruments include a body (arm) movable in the directions of axes of coordinates of a spatial rectangular coordinate system, that is, X, Y and Z axes which are perpendicular to each other, and a needle provided on the movable body. The needle contacts with a detection point of an outer profile of a subject for measurement to detect three-dimensional coordinates of the movable body upon such contacting to measure a three-dimensional profile.
However, with such contacting three-dimensional measuring instruments, where the subject for measurement is molded from a soft material such as, for example, clay, when an end of the needle is contacted with the detection point of the subject for measurement, the end is liable to bite into the subject for measurement so that an error is produced in detected coordinates of the subject for measurement. There is the possibility that concave and convex measurements may be produced on the outer profile of the subject for measurement.
In order to eliminate such a disadvantage, the three-dimensional measuring instrument should be of the non-contacting type wherein, for example, a laser light source and a light receiving element are used for receiving a reflected laser beam, the distance between the subject for measurement and the laser light source is measured and, at a point in time when the distance reaches a predetermined value, coordinates of the detection point of the subject for measurement are measured.
With a contacting three-dimensional measuring instrument, when the needle is directed perpendicularly to a predetermined position of the surface of a subject for measurement, coordinates of the position can be detected accurately. Accordingly, in such a non-contacting three-dimensional measuring instrument as described above, detection of coordinates is performed using such a customary technique.
The technique of detection of coordinates described above is described with reference to FIGS. 7(a) and 7(b). Referring to FIGS. 7(a) and 7(b), the Y-axis is disposed in a direction perpendicular to the plane of the figure. A subject for measurement 100 is provided adjacent to a laser unit 10 having a laser light source and a light receiving element for a laser beam disposed therein for detecting the distance to the subject 100 for measurement in a non-contacting condition.
The structure of the laser unit 10 is shown in FIG. 12. Laser light radiated from a semiconductor laser 12, which is a light emitting element, is irradiated upon the subject 100 for measurement. When the subject 100 for measurement is disposed at a reference point Lref (for example, at the distance of 50 mm in the laser light irradiation direction from the laser light irradiation position of the laser unit 10), laser light reflected at random from a detection point of the subject 100 for measurement is received at a central position of a light receiving element 15. Further, when the position of the subject 100 for measurement is nearer (100A) or farther (100B) than the reference point, Lref, the light receiving position of laser light on the light position detecting element 15 moves in the direction of an arrow mark A or B. The output of the light position detecting element 15 is outputted to a first signal processing circuit 50, as illustrated in FIG. 6.
When measurement is performed using such a laser unit 10, as shown in FIG. 7(a), the mounting position of the laser unit 10 is set so that laser light 10A irradiated from the laser unit 10 is irradiated substantially perpendicularly upon a portion (detection point) of the subject 100 for measurement whose coordinates are to be detected, and thereafter, the laser unit 10 is fed in the X and Z directions simultaneously so that the laser unit 10 may move in the irradiation direction (the direction of an arrow mark L) of the laser light. When the laser unit 10 is moved closer to the subject 100 for measurement as shown in FIG. 7(b), laser light 10B reflected from the subject 100 for measurement is detected by way of a lens system. When the light detected from a result of the detection that the laser unit 10 comes to a predetermined distance from the laser unit 10, coordinate data of the laser unit 10 or of an arm (not shown) which supports the laser unit 10 thereon are then collected as coordinate data corresponding to the laser light irradiation position (detection point) of the subject 100 for measurement.
As illustrated in FIGS. 19(a) to 19(c), a light emitting portion 101A and a light receiving portion 101B are provided for the laser light. As shown in FIG. 19(a), the mounting position of the laser unit 101 is set so that laser light irradiated from the light emitting portion 101A of the laser unit 101 is irradiated substantially perpendicularly upon a portion of the subject 100 wherein the coordinates are to be measured. Thereafter, the laser unit 101 is fed in the X and Z directions simultaneously so that the laser unit 101 may move in the irradiation direction (the direction of an arrow mark L) of the laser light. When the laser unit 101 is moved closer to the subject 100 for measurement as shown in FIG. 19(b), laser light reflected from the subject 100 for measurement is detected by way of a lens system provided at the light receiving portion 101B. When the light is detected from a result of the detection that the laser unit 101 has arrived at a predetermined distance from the laser unit 101, coordinate data of the laser unit 101 or of an arm (not shown) which supports the laser unit 101 thereon is collected as coordinate data corresponding to the laser light irradiation position of the subject 100 for measurement.